Competitive immunochromatographic assay for the detection of the organophosphorus pesticide EPN

An immunochromatographic assay (ICA) based on competitive antigen-coated format and colloidal gold label was developed for the detection of the organophosphorus insecticide O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN). The ICA test strip consisted of a membrane with a detection zone, a sample pad and an absorbent pad. The membrane was separately coated with EPN hapten-OVA conjugate (test line) and anti-mouse IgG (control line). As the competition is between the migrating analyte and the immobilised analyte hapten for the binding sites of the migrating antibody–colloidal gold (Ab–CG) conjugate, this study suggests that the relative migration speed between the two migrating substances is a critically important factor for the sensitive detection by competitive ICA. Based on this criterion, a nitrocellulose (NC) membrane was chosen as the most suitable for EPN ICA. The detection limit of the ICA for EPN standard and EPN spiked into agricultural samples were 10−2 and 5×10−2 µg mL−1, respectively.